Code carriers of the magnetic disc type are generally driven by driving means known in the prior art which comprise a shaft having a pulley on one end and a conical part at the other end. The shaft is mounted in a bearing assembly. The code carrier usually takes the form of a magnetic disc with a center opening that is fitted over the aforesaid conical part in order to properly center the disc. The disc is furthermore clamped between a movable holder and a further holder which is associated with the shaft in order to rotate the disc with the shaft.
A serious disadvantage of the above-described assembly is that the magnetic disc must be moved axially in a direction over the conical part before it can be removed in a radial direction, thus making it slower and more difficult to exchange magnetic discs. In addition, the construction of the drive mechanism is more complicated than should be necessary.
An object of the present invention is to construct a drive assembly for a disc-shaped code carrier in which discs can be replaced, or a disc can be exchanged for another disc without affecting the other disc.
A further object of the present invention is to provide a drive mechanism with a rotatable drive element having at least one contact surface co-acting with a code carrier and being provided with at least one guide surface.
Another object of the present invention is to provide at least one centering device that is movable in the axial direction of the drive element and is provided with a further guide surface, which co-acts with the guide surface of the drive element as well as the central opening in the code carrier.
The drive mechanism is further provided with a retaining member by which the code carrier can be firmly held against the contact surface of the drive element.